1. Field of the Invention
The present invention relates to a differential amplifier and a display driver including the differential amplifier.
2. Description of the Related Art
A display driver for driving a display panel, for example, a liquid crystal display panel, includes a plurality of amplifiers that apply gradation voltages having voltage values corresponding to luminance levels represented by an input video signal to respective data lines in the liquid crystal display panel.
As an amplifier for such a display driver, a differential amplifier (operational amplifier) has been proposed (see Japanese Patent Application Laid-open No. Hei. 11-249623, for example). In the differential amplifier, however, an offset is generated due to the influence of manufacturing variations, for example. Thus, when the differential amplifier is employed as an amplifier for a display driver, such an offset leads to a deterioration in a displayed image. In view of this, according to such a display driver, in supplying an input voltage to one of an inverting input terminal and a non-inverting input terminal of the differential amplifier and supplying an output voltage to the other terminal, the input terminals (the inverting input terminal and the non-inverting input terminal) to which the input voltage and the output voltage are supplied are interchanged with each other every predetermined period. This achieves reduction in average value of offsets contained in the output voltages on a long-term basis, i.e., offset cancelation.
According to the above offset cancelation method, however, an output voltage including a positive offset and an output voltage including a negative offset are alternately output as they are. Therefore, offsets may not be sufficiently averaged depending on its transition period. Thus, if a display panel is driven by the display driver employing the amplifiers having such an offset cancelation function, there is a risk of causing a deterioration in image quality such as flickering on a display screen.